<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>1px 问题</title>
    <style>
        .box {
            width: 100px;
            height: 100px;
            background-color: white;
            position: relative;
            outline: 1px solid red;
        }
        .box::after {
            content: '';
            position: absolute;
            bottom: 0;
            left: 0;
            right: 0;
            height: 1px;
            background-color: black;
            transform: scaleY(0.5);
            transform-origin: center bottom;
        }
    </style>
</head>
<body>
    <div class="box"></div>
</body>
</html>